SC4524B_08 Datasheet, PDF (14/18 Pages) Semtech Corporation – 18V 2A Step-Down Switching Regulator

C₅
=
2
π
⋅

6
⋅

0

3
⋅
2
2
.
⋅

0
3
= 0.45nF
C₈
=
2
π⋅
6
00
⋅

0 ³
⋅ 22. ⋅0 ³
= 2pF
SC4524B
Applications Information (Cont.)
(230)%Ploafc^VV_te^oc_he⁼thc₍e_{roc+sossom/vp}^G_eωer^Ppn^W_f)r^Ms_(ea⁽_q^t₊ou⁺re_{s n}^s/z^R_ceωyr^Eno,^S_Q^R_F, ^C_CF_+.^O_Z1s),2b_/e_ωtw_{n2 )}een 10% and
capacitor, the main power switch and the freewheeling
diode carry pulse current (Figure 9). For jitter-free
(4) Use the compensator pole, F_P1, to cancel the ESR zero, ^{operation, the size of the loop formed by these components}
F_Z.
(5)
The^Gn^P,^Wt^Mhe^≈
p_Ga_Cr_A^Ra_â‹m_{R S}et^, ers
can be calculated by
of
the^ωpco^≈m_Rp^Ce_On^,sation
ne^ωtw^Zo⁼rk_{R ES}^_RC^sitnhh_O^{teoe, ugfrlredaetbweedhemweiiltnihnimignidztheioded.SeSCicn4loc5e2se4tBhto,ectpohonewnneeecrgtisanwtgiivttechhteeirsamnaoilnrdeaealdooyff}
AC
R₇
= ^{0 20}
g_m
the input bypass capacitor minimizes size of the switched
current loop. The input bypass capacitor should be placed
close to the IN pin. Shortening the traces of the SW and
C₅
=

2 πF_Z
R₇
C₈
=

2 πF_P
R₇
where g_m=0.28mA/V is the EA gain of the SC4524B.
BST nodes reduces the parasitic trace inductance at these
nodes. This not only reduces EMI but also decreases
switching voltage spikes at these nodes.
The exposed pad should be soldered to a large ground
plane as the ground copper acts as a heat sink for the
device. To ensure proper adhesion to the ground plane,
Example: Determine the voltage compensator for an ^{avoid using vias directly under the device.}
800kHz, 12V to 3.3V/2A converter with 22uF ceramic
output capacitor.
V _IN
Choose a loop gain crossover frequency of 80kHz, and
p(r2el_A0aqCc%u₌eir_{−evoA2dof0C}lct_⋅F=lao_oCg_{gm)−,eGp2aC}ce_0AnoRndâ‹m_Sslaoâ‹pF_{2tgoePπ1Frn=GCgsC6aCaO0A}ti_Ro0_⋅nVkVr_SFaOHBzt_{⋅zeF2.rC}o_{πFiFsraConCmdO} p_⋅EoVqVl_FuOe_{Ba}atitonF_{Z1(=91),6ktHhez}
VOUT
A_C
=
−_A2 0_C
⋅₌log_{−}

20
28 ⋅
6^â‹.^l^o⋅^g^{}0
2^−38^â‹
2_â‹
π₆⋅_.

⁸⁰⋅^â‹^0^{0 3−⋅32}
⋅
2
2^{⋅ }π⁰
−_â‹6₈^â‹₀^3.._â‹⁰³_^{}₀^=₃^
5 . 9 dB
⋅ 22
⋅

0
−6
⋅
.0
3.3

=
5
.9
dB
ZL
Then the c_5o_.9 mpensator parameters are
R₇
C₅
=
=
0
0 ²⁰
.28 ⋅0 ^−3
R₇ = _0.
= 22.53.9k
0 ²⁰
2^8 ⋅ 0
−3
2π ⋅6 ⋅0 ³ ⋅ 22. ⋅0 ³
=
=
22.3k
0 . 4 5 nF
C₈
=
C₅
2 π⋅ 6
=
00

2_⋅π₀ ³â‹…
_{⋅ 2}6₂

.^â‹^⋅⁰ 0^{3 3}
⋅
=₂₂2_.p_F
⋅

0
3
= 0.45nF
V_o
V_c
=
C₈
( + s
=_{GP2WMπ(⋅ 6+0sR0ES⋅RC0O)}^₃
/ ω_p )( + s / ω_n Q + s ²
⋅ 22.
/ ω_n2 )
⋅0
3
= 2pF
Select R₇=22.1k, C₅=0.47nF, and C₈=10pF for the design.
Figure 9. Heavy lines indicate the critical pulse
current loop. The inductance of this
loop should be minimized.
Car^Goe^Pm^W_l^M_ips^≈_tee^VVGnd^oc_Cs_A^R=ai⋅_nRto_(STr^,_a+bplaser/a4^Gm_{ω. A}^Pω_pe^Wp₎tM^M₍e^≈_(raR^s₊^_tC_h⁺f_OsoC^,s/rA^R_ωvD^Ea_nSr_Q^R_pio^C_r+ou^Oω_gss^)Z_2rt⁼_ay/R_mpωEi_S^c_Rin2sCa_)Oal ^,_{laspopalivcaaitlaiobnles}
AC
up_PRpa_CC7r5o_Ba==nm_L^2r_{ag0GeeπmytF}²q_P⁰_eoZWu_ruMRset.7s_≈Ct f_oGo_nCr_AsRd_i⋅de_Rt_eSa_ri_,ale_td_ioc_na_slcul_ωat_pio_≈n_Ro_Cf
the
,
O
compensator
ω_Z = _R
E

SR
C
O
,
C
In
8⁼
a

AC
s²tR^πe^F₇p^P=-^Rd^7o_g0w_m²n⁰
switching
regulator,
the
input
bypass
C₅
=^
2 πF
R
Vin
Cu
+
14